Please identify a quantitative research article evaluating mediation in your field and provide the citation.
Bucagu, M., Bizimana, J. de D., Muganda, J., & Humblet, C. P. (2013). Socio-economic, clinical and biological risk factors for mother - to – child transmission of HIV-1 in Muhima health centre (Rwanda): a prospective cohort study. Archives of Public Health, 71(1), 4. https://ucsf.idm.oclc.org/login?url=http://doi.org/10.1186/0778-7367-71-4
What is the primary discipline of the authors?
Public Health, Statistics, Applied Mathematics, and Medicine (Obstetrics & Gynecology and Maternal, Newborn and Child Health)
Draw a DAG representing the implicit or explicit causal model explored in this paper (you do not need to post your DAG, but we will try to discuss in class).
What is the exposure of interest?
Marital status of mother
What is the outcome of interest?
Infant HIV-1 status at 6 weeks of age
What is the hypothesized mediator of interest and how is it measured?
Disclosure of HIV status to partner.
All data was collected from the women themselves and logbooks in the health center using a structured questionnaire.
Describe the modeling approach and briefly report the estimated total, direct, and indirect effects (if these are reported).
A series of multivariable logistic regression models were used to quantify the relationships between 1) marital status and disclosure, 2) marital status and infant HIV-status, and 3) disclosure and infant HIV-status.
Marital status has shown no effect on infant HIV status when disclosure was controlled. The risk of infant HIV infection at 6 weeks was higher in unmarried (adjusted OR of 1.42 with a 95%CI 0.29-4.08) vs. married (reference) women with undisclosed HIV status as the mediator.
If the direct effect is reported, would you describe this as a natural direct effect, a controlled direct effect, or something else?
The direct effect is not reported quantitatively, but it is stated that the independent variable (martial status) has no effect on the dependent variable (infant HIV-status), therefore this is a controlled direct effect.
Do you think there is potential measurement error in the mediator and how would that affect the results?
Given that the mediator is binary (married vs. unmarried), I don’t believe there is much potential for measurement error. The only issue may be the self-reported nature of this information.
Do you think there are unmeasured confounders of the mediator-outcome association and how would that affect the results of the mediation analysis?
I’m not totally convinced that disclosure is the most important variable to consider as a mediator in this situation because since the mother is already HIV+, this would have no biological effect on the transmission of HIV to her infant. However, disclosure might be an indicator of health seeking behavior.
Do you have any critiques of the paper?
Given that all the predictors of MTCT were entered into the model and included if they had a p-value of <0.05 using the Hosmer and Lemeshow test, and they considered a wide variety of predictors, it feels like the authors were doing a bit of fishing.